Notion of (in)finite predicates

See merge request !56

Additionally lemmas for insert, nth, take, and list_find

See merge request !55

Rename multiset "union" into "disjoint union"

Closes #13

See merge request !57

Also, use the union name/class/symbol for what's usually the union, and
define the intersection on multisets.

fix or silence Coq 8.10 warnings

See merge request !52

New `seq` operation on maps + consistency tweaks for `seq` operation on sets

See merge request !44

Consistently use `set_` prefix.

Closes #24

See merge request iris/stdpp!45

- Rename `gmap.to_gmap` into `gset_to_gmap`.
- Rename `gmap.of_gset` into `gset_to_propset`.
- Rename `coPset.to_Pset` into `coPset_to_Pset`.
- Rename `coPset.of_Pset` into `coPset_to_gset`.
- Rename `coPset.to_gset` into `coPset_to_gset`.
- Rename `coPset.of_gset` into `gset_to_coPset`.

The following `sed` script can be used for the first rename:

```
sed -i 's/to\_gmap/gset\_to\_gmap/g' $(find ./theories -name \*.v)
```

The latter is context sensitive, so was done manually.

Get rid of using `Collection` and favor `set` everywhere. Also, prefer conversion
functions that are called `X_to_Y`.

The following sed script performs most of the renaming, with the exception of:

- `set`, which has been renamed into `propset`. I couldn't do this rename
  using `sed` since it's too context sensitive.
- There was a spurious rename of `Vec.of_list`, which I correctly manually.
- Updating some section names and comments.

```
sed '
s/SimpleCollection/SemiSet/g;
s/FinCollection/FinSet/g;
s/CollectionMonad/MonadSet/g;
s/Collection/Set\_/g;
s/collection\_simple/set\_semi\_set/g;
s/fin\_collection/fin\_set/g;
s/collection\_monad\_simple/monad\_set\_semi\_set/g;
s/collection\_equiv/set\_equiv/g;
s/\bbset/boolset/g;
s/mkBSet/BoolSet/g;
s/mkSet/PropSet/g;
s/set\_equivalence/set\_equiv\_equivalence/g;
s/collection\_subseteq/set\_subseteq/g;
s/collection\_disjoint/set\_disjoint/g;
s/collection\_fold/set\_fold/g;
s/collection\_map/set\_map/g;
s/collection\_size/set\_size/g;
s/collection\_filter/set\_filter/g;
s/collection\_guard/set\_guard/g;
s/collection\_choose/set\_choose/g;
s/collection\_ind/set\_ind/g;
s/collection\_wf/set\_wf/g;
s/map\_to\_collection/map\_to\_set/g;
s/map\_of\_collection/set\_to\_map/g;
s/map\_of\_list/list\_to\_map/g;
s/map\_of\_to_list/list\_to\_map\_to\_list/g;
s/map\_to\_of\_list/map\_to\_list\_to\_map/g;
s/\bof\_list/list\_to\_set/g;
s/\bof\_option/option\_to\_set/g;
s/elem\_of\_of\_list/elem\_of\_list\_to\_set/g;
s/elem\_of\_of\_option/elem\_of\_option\_to\_set/g;
s/collection\_not\_subset\_inv/set\_not\_subset\_inv/g;
s/seq\_set/set\_seq/g;
s/collections/sets/g;
s/collection/set/g;
' -i $(find -name "*.v")
```

Confluent relations

See merge request !53